Children and youth with developmental disabilities (DD) receive extensive pediatric rehabilitation services to address functional limitations in self-care, mobility, and socialization. The Patient Protection and Affordable Care Act mandates the inclusion of the patient's perspective in healthcare evaluation. Yet, there is a lack of self-reported healthcare assessments appropriate for youth with DD. To accurately self-report, youth must execute numerous cognitive processes involving attention, working memory, long term memory, and judgment. The cognitive and literacy deficits of youth with DD make common formats for soliciting self-reports--written, paper and pencil assessments--inaccessible to most youth with DD. Technology, such as AbleLink's ATLAS software, has been demonstrated to scaffold these cognitive processes and help youth to provide reliable self-reports. The proposed STTR Phase I will harness technology to develop the first PRO software designed to bolster the validity and reliability of self-reports by youth with DD: the PEDI-PRO. This project will: 1) Identify initial system specifications that operationalize the requirements of an accessible PEDI-PRO software platform. 2) Refine specifications to maximize the usability and cognitive accessibility of the prototype PEDI-PRO with a clinical sample, and 3) Demonstrate the reliability of the prototype PEDI-PRO when used by transition-age youth with DD ages 14-25. This study will use an iterative design and evaluation process to develop the PEDI-PRO prototype in collaboration with a Youth Panel and Advisory Board. First, the Advisory Board and Youth Panel will select questions to include in the initial prototype and generate software requirements for a PEDI-PRO user interface. These requirements will guide the creation of PEDI-PRO System Requirements and Specifications and the prototype design. When appropriate, the ATLAS software platform will be customized to meet these requirements and support the PEDI-PRO's workflow. Second, we will use think-aloud cognitive interviews and document usability heuristics with youth with DD (n = 15) and conduct system usability scale (SUS) surveys with clinicians (n = 15). The prototype will be refined based on results. Third, youth with developmental disabilities (n = 45) will complete the PEDI-PRO twice in a two week time period to determine the consistency of self-reports over time. If results are positive, Phase II would incorporate all PEDI-PRO questions into the prototype and expand testing to a large sample (250+) to take the first steps towards a computer-adaptive testing approach.